It's recommended to change the Sync Shift Time from default of 30% of cycle time to 10-20%. From I/O Devices > Device > EtherCAT > Advanced:
Distributed Clocks > SYNC Shift Time:
This prevents an issue where there's a lag in the cycle which affects positioning:
Note this is using C3_EtherCAT_full_2ms_V204.xml
This file is available on the Compax3 DVD that ships with the products.